The present invention relates, in general, to electronics and, more particularly, to a brushless DC motor.
Brushless Direct Current (BLDC) motors are used in a variety of applications including disc drives, compact disc players, digital video disc players, scanners, printers, plotters, actuators used in the automotive and aviation industries, etc. Typically, multiple phase motors include a stationary portion or stator that produces a rotating magnetic field and a non-stationary portion or rotor in which torque is created by the rotating magnetic field. The torque causes the rotor to rotate which in turn causes a shaft connected to the rotor to rotate. At start-up it is desirable to detect the position and rotation rate of the brushless DC motor's rotor. In a brushless DC motor having sensors, the rotor position and its rotation rate may be detected and controlled using a detection circuit that includes at least one Hall sensor and at least one comparator. However, the accuracy of the detection circuit is influenced by its operating environment, which may decrease the accuracy of the position and rotational speed measurements. For example, the inherent offset of the comparator typically introduces an undesirable level of offset in the output signal from the comparator. In addition, a Hall comparator usually has an inherent DC offset temperature drift that affects the output voltage of the comparator, which introduces further inaccuracies in the position and rotational speed measurements. Another drawback with sensor-less BLDC motors is that they may not handle applications that include large input voltage ranges, e.g., a range from zero volts to twenty-eight volts.
Accordingly, it would be advantageous to have a method and structure for detecting a rotor position and rotational rate that is accurate at motor start-up and during low rotational speeds over large temperature excursions. It is desirable for the method and structure to be cost and time efficient to implement.
For simplicity and clarity of illustration, elements in the figures are not necessarily to scale, and the same reference characters in different figures denote the same elements. Additionally, descriptions and details of well-known steps and elements are omitted for simplicity of the description. As used herein current carrying electrode means an element of a device that carries current through the device such as a source or a drain of an MOS transistor or an emitter or a collector of a bipolar transistor or a cathode or an anode of a diode, and a control electrode means an element of the device that controls current flow through the device such as a gate of an MOS transistor or a base of a bipolar transistor. Although the devices are explained herein as certain n-channel or p-channel devices, or certain n-type or p-type doped regions, a person of ordinary skill in the art will appreciate that complementary devices are also possible in accordance with embodiments of the present invention. It should be noted that a doped region may be referred to as a dopant region. It will be appreciated by those skilled in the art that the words during, while, and when as used herein are not exact terms that mean an action takes place instantly upon an initiating action but that there may be some small but reasonable delay, such as a propagation delay, between the reaction that is initiated by the initial action and the initial action. The use of the words approximately, about, or substantially means that a value of an element has a parameter that is expected to be very close to a stated value or position. However, as is well known in the art there are always minor variances that prevent the values or positions from being exactly as stated. It is well established in the art that variances of up to about ten percent (10%) (and up to twenty percent (20%) for semiconductor doping concentrations) are regarded as reasonable variances from the ideal goal of exactly as described.